Besides teaching himself the Lord also sent out the Twelve in pairs. The reason for sending them in pairs was so that they would go more readily, for they might not have been so willing to set out all alone, and, on the other hand, if he had sent more than two together, there would not have been enough apostles to cover all the villages. So he sent them two by two: “two are better than one,” as Ecclesiastes says.
He commanded them to take nothing with them, neither bag, nor money, not bread, so as to teach them to despise riches, and to make people ashamed when they saw them preaching poverty by their own lack of possessions. For who would not blush for shame, strip himself of his possessions, and embrace a life of poverty when he saw an apostle carrying neither bag, nor even bread which is so very essential?
The Lord instructed them to stay in the same house so as not to give the appearance of restlessness, as though they moved from one family to another in order to satisfy their stomachs.
On the other hand, he told them to shake the dust off their feet when people refused to receive them, to show that they had made a long journey for their sakes and they owed them nothing; they had received nothing from them, not even their dust, which they shook off as a testimony against them—a testimony of reproach. “Be sure of this, I tell you: Sodom and Gomorrah will fare better on the Day of Judgment” than those who will not receive you. The Sodomites were punished in this world, so they will be punished less severely in the next. What is more, no apostles were sent to them. For those who refused to receive the apostles greater sufferings are in store.
“So they set out to preach repentance. They cast out many demons, and anointed many sick people with oil and cured them.”
The fact that the apostles anointed the sick with oil is mentioned only by Mark, but the practice is also referred to in his general letter by James, the brother of the Lord, who says: “Are there any sick people among you? Let them send for the elders of the Church and let these pray over them, anointing them with oil.” Oil is beneficial for the relief of suffering, and it also produces light and makes for cheerfulness. It symbolizes the mercy of God and the grace of the Spirit, through which we are freed from suffering and receive light, gladness, and spiritual joy.
St Theophylact of Ochrid